Packaging material made of biaxially oriented polyolefin film

ABSTRACT

The invention relates to a packaging material made of a multilayer oriented polyolefin film, which comprises a base layer and at least one first outer layer, whereby the first outer layer is placed in contact with itself or in contact with the opposing surface of the film or in contact with the surface of another film. This first outer layer contains an additive which absorbs light within the wavelength range of a laser such that when the film is locally irradiated by the laser, the area of irradiation experiences an increase in temperature that causes the polyolefin of the first outer layer to soften or melt in the irradiated area and to bond to another layer when cooled.

The invention relates to packaging made of a biaxially orientedpolyolefin film.

Polyolefin films are widely used as packaging films. The success ofthese materials is based on the good optical and mechanical propertiesand on the simple weldability of the films. Besides welding,heat-sealing of films has increased in importance. Heat-sealable filmshave an outer layer of a polymer which has a lower crystallite meltingpoint than the polymer of the base layer. For heat-sealing, the filmlayers are laid one on top of the other and warmed to only from 10 to20° C. below the crystallite melting point, i.e. the outer layers arenot completely melted. The adhesion of the heat-sealing layers which isachieved is significantly less than in the case of welding of the samematerial, but is sufficient for many applications (Kunststoff-Handbuch[Plastics Handbook], Volume IV, Carl Hanser Verlag, Munich, 1969, pages623 to 640).

Besides the use of heat-sealable layers, the application of so-calledcold-sealing layers is known. Cold-sealing layers are used, inparticular, where heat-sensitive package contents, such as, for example,chocolate, are packaged in film. The application of cold-sealing layersis an additional processing step which considerably increases the costsfor a package.

Independently of these packaging technologies, such as welding,heat-sealing or cold-sealing, processes for marking polymeric materialshave been developed in recent years. Materials of this type contain aradiation-sensitive additive which causes a colour change in thematerial on exposure to radiation in certain wavelength ranges. Suitableadditives for this application are, for example, laser pigments.

In addition, the prior art discloses processes for joining plasticcomponents by means of lasers, in which the thermal and mechanical loadon the components is low. For many applications, transmission laserwelding has become established. In this method, the laser beam passesthrough a transparent component unhindered and hits the laser-absorbentjoin partner. The action of the laser beam causes the plastic of theabsorbent partner to melt at the surface and join to the join partner oncooling. In this process, diode lasers or solid-state lasers havingwavelengths in the near infrared region are employed.

The object of the present invention therefore consisted in providingpackaging made of a polyolefin film which avoids the disadvantages ofcold-sealing coating, but is equally suitable for the packaging ofheat-sensitive products.

This object is achieved by packaging made of a multilayered, orientedpolyolefin film which comprises a base layer and at least one firstouter layer, where this first outer layer is in contact with itself orin contact with the opposite surface of the film or in contact with thesurface of a further film, characterized in that the film comprises inthis first outer layer an additive which has an absorption in thewavelength range of a laser such that, on local irradiation of the filmwith this laser, a temperature increase occurs in the area of theirradiation such that the polyolefin of the first outer layer softens ormelts in the irradiated area and bonds to a further layer on cooling.The subclaims indicate further embodiments of the invention.

A further object of the present invention consisted in indicatingadvantageous packaging comprising a container with lid.

This object is achieved by packaging made of a multilayered, orientedpolyolefin film which comprises a base layer and at least one firstouter layer, where the polyolefin film comprises in the first outerlayer an additive which has an absorption in the wavelength range oflasers such that, on local irradiation of the film with a laser, atemperature increase occurs in the area of the irradiation such that thepolyolefin of the first outer layer softens or melts therein in theirradiated area and bonds to a further layer on cooling.

Besides the laser-absorbent pigment, the outer layer of the filmgenerally comprises at least 80% by weight, preferably from 85 to <100%by weight, in particular from 90 to 98% by weight, in each case based onthe layer, of a polyolefin.

Examples of suitable olefinic polymers of the outer layer are

propylene homopolymers

ethylene homopolymers

copolymers of

ethylene and propylene or

ethylene and 1-butylene or

propylene and 1-butylene or

terpolymers of

ethylene and propylene and 1-butylene or

a mixture or blend of two or more of the said homopolymers, co-polymersand terpolymers,

particular preference being given to

random ethylene-propylene copolymers having

an ethylene content of from 1 to 10% by weight, preferably from 2.5 to8% by weight, or

random propylene-1-butylene copolymers having

a butylene content of from 2 to 25% by weight, preferably from 4 to 20%by weight,

in each case based on the total weight of the copolymer, or

random ethylene-propylene-1-butylene terpolymers having

an ethylene content of from 1 to 10% by weight, preferably from 2 to 6%by weight, and a 1-butylene content of from 2 to 20% by weight,preferably from 4 to 20% by weight, in each case based on the totalweight of the terpolymer, or

a blend of an ethylene-propylene-1-butylene terpolymer and apropylene-1-butylene copolymer

having an ethylene content of from 0.1 to 7% by weight

and a propylene content of from 50 to 90% by weight

and a 1-butylene content of from 10 to 40% by weight,

in each case based on the total weight of the polymer blend.

The above-described copolymers and/or terpolymers employed in the outerlayer generally have a melt flow index of from 1.5 to 30 g/10 min,preferably from 3 to 15 g/10 min. The melting point is in the range from120 to 140° C. The above-described blend of copolymers and terpolymershas a melt flow index of from 5 to 9 g/10 min and a melting point offrom 120 to 150° C. All the above-mentioned melt flow indices aremeasured at 230° C. and a force of 21.6 N (DIN 53 735).

The propylene homopolymers employed in the outer layer generally have amelt flow index of from 1.5 to 30 g/10 min, preferably from 3 to 15 g/10min. The melting point of the homopolymers is in the range from 150 to170° C., preferably from 155 to 165° C. Preference is given to isotactichomopolymers whose isotacticity is greater than 92%, preferably in therange from 94 to 98%. The n-heptane-soluble content of the isotacticpropylene homopolymers is less than 10% by weight, preferably from 1 to8% by weight, based on the weight of the homopolymer. All theabove-mentioned melt flow indices are measured at 230° C. and a force of21.6 N (DIN 53 735).

If desired, conventional additives, such as antistatics, neutralizers,lubricants and/or stabilizers, and, if desired, additionallyantiblocking agents in effective amounts in each case may be added tothe outer layer(s).

It is essential to the invention that the absorbent outer layer of thefilm comprises an additive which absorbs radiation in the wavelengthrange of lasers. Additives of this type are referred to below for thepurposes of the present invention as pigments or laser pigments.

The incorporation of laser pigments of this type into the outer layer ofthe film results in absorption of the radiation, i.e. a take-up ofenergy, on irradiation of the film. It is known in the prior art that,given an appropriate wavelength, the laser beam leaves behind a visibletrack in the form of a white or coloured line in the pigmented plastic.This effect is utilized for marking plastic components and plastic filmsby means of a laser. As part of the present invention, it has now beenfound that irradiation of films laid one on top of the other by means ofa laser beam produces a strong connection between the two film layers,in a similar manner to a heat-seal or weld seam, if at least one of thetwo films has a laser pigment-containing outer layer and this laserpigment-containing layer is facing the second films in such a way thatthe pigmented outer layer is in contact with the second film layer. Ithas been found here that it is particularly advantageous for theproduction of a seal seam for both outer layers in contact to comprise acorresponding, preferably the same, absorbent pigment.

Surprisingly, the laser beam passes through the other layers of the filmwithout leaving behind visible tracks there, as is known from lasermarking, and without leaving behind other damage. It was unexpected thatthe laser absorption would be so pronounced that the film absorbssufficient energy for softening or warming of the outer layer. Inparticular, it was questionable whether the absolute amount of laserpigments in the thin outer layer would be sufficient to facilitateuniform melting of the outer layer through absorption. At the same time,it has been found that the warming or melting of the outer layer remainsrestricted very locally to the irradiated area. This makes it possible,for the production of packaging, to incorporate a lasered seal seamspecifically where this seam is desired.

Thermal loading of the packaged product by the laser beam isadvantageously avoided here. The new technology is therefore suitablefor replacing known cold-sealing coatings for the packaging ofheat-sensitive products.

The laser pigment-containing outer layer may be applied both to opaqueand transparent films known per se, or to their base layer orinterlayer. For opaque or white films, it was particularly surprisingthat the fillers of the other layers, which serve for opacification orwhite coloration of the film, do not hinder absorption of the laserradiation in the pigmented outer layer and warming of the laserpigment-containing outer layer. The absorption in the filler- and/orpigment-containing layers is so low, or does not occur, that noimpairment of the laser sealing or film integrity or the other filmproperties by the laser beam has been noted.

For the purposes of the present invention, laser pigments areincompatible particles which are inert towards the matrix polymer and donot result in any significant vacuole formation during stretching. Themean particle size of the laser pigments is generally in a range from0.01 to 4 μm, preferably in the range from 0.1 to 2 μm, in particularfrom 0.1 to 1 μm. The outer layer generally comprises laser pigment inan amount of from 0.01 to 10% by weight, preferably from 0.5 to 5% byweight, in particular from 0.8 to 3% by weight, based on the weight ofthe outer layer. If the concentration of the laser pigments is too low,only moderate absorption of the laser beam takes place, which results inpoor seal strength. A high concentration of laser pigments does notachieve any additional effects with respect to the laser absorption. Athigh concentrations of coloured, metal and black pigments, a coloureffect (grey effect) occurs which may be disadvantageous, but may bedesired for some applications.

The laser pigments used are preferably metal pigments, such as aluminiumor copper or tin pigments, or copper alloys, such as, for example,copper/zinc or copper/tin alloys, and black and coloured pigments, inparticular carbon black or graphite, iron oxides, rutile mixed phases,ultramarines, spinels and zirconium silicates. Of the above-mentionedpigments, aluminium pigments, copper/zinc alloys and carbon black andgraphite are particularly preferred. It has been found that in the caseof carbon black a content of between 0.1 and 1.0% by weight, in the caseof aluminium pigments a content of from 0.5 to 1.5% by weight and in thecase of copper alloys a content of from 0.5 to 3.0% by weight,preferably from 1 to 2% by weight, based on the weight of the outerlayer, are particularly advantageous.

The above-mentioned laser-absorbent metal, black or coloured pigmentsmay, if desired, be employed in the form of a mixture with metal oxides,such as white pigments, for example titanium dioxide, aluminium oxide,silicon dioxides, corresponding metal hydroxides and metal oxidehydrates, and carbonates and silicates, such as, for example, calciumcarbonate, aluminium silicate (kaolin clay), magnesium silicate (talc)or mica.

The pigment mixtures are advantageous since they firstly have a broadabsorption spectrum, particularly in the wavelength range of the lasersused. Secondly, the high absorption capacity of the laser-absorbentmetal, black or coloured pigments is utilized and at the same time thecolourings by these laser-absorbent pigments are lightened again bymeans of corresponding white pigments. The light-scattering action ofthese white pigments intensifies the absorption properties of the metal,black and coloured pigments here and favours the build-up of heat in theouter layer.

The mixing ratio of white pigments and black, metal or coloured pigmentscan vary in broad ranges and enables an optimum absorption range to beset, depending on the laser used. In addition, the mixtures enable thedesired hue of the film to be set. If desired, the mixture can beexpanded to give a system comprising a plurality of components. Forexample, the ratio of white pigment to black, metal or coloured pigmentsis in a range from 5:1 to 1:5, with TiO₂ preferably being employed inthe mixtures as lightening white pigment.

The pigment mixtures are mixed homogeneously by means of suitablemethods, for example by ball grinding. At the same time, the suitablemean particle size and the suitable distribution width of the particlesize can be set.

Furthermore, the pigments or pigment mixtures can be coated in order,for example, to produce improved adhesion to the polymer matrix andeffectively to prevent cracks and vacuole formation, as are known ofvacuole-initiating particles, during stretching. Coating, for examplewith resins or waxes, is particularly advantageous for the metalpigments, such as, for example, aluminium powder. This also preventsundesired dust formation, which may be hazardous to health and anexplosion risk. In addition, these wax coatings improve thedispersibility of the pigments in the polymer (deagglomeration) and thegood meterability of the pigments in masterbatch preparation. Ingeneral, commercially available metal pigments are already provided withwax and/or resin coatings of this type. Processes for the production ofpigment coatings of this type are known in the prior art. In these, thepigments are wetted by these low-viscosity waxes or resins and, ifdesired, moistened through, which is advantageous for thedispersibility.

The pigments can have a spherical or columnar or leaf-shaped habit. Thesize, geometry and orientation of the particles may have an effect onthe absorption behaviour to laser beams.

In a preferred embodiment, the polyolefin film according to theinvention has a further second outer layer comprising polymers ofolefins having from 2 to 10 carbon atoms which is applied to the sideopposite the laser pigment-containing layer. In a preferred embodiment,this second outer layer is of such a composition that it absorbsessentially no radiation in the wavelength range of the lasers used forthe sealing. For the production of the packaging according to theinvention, it is essential that the laser beam passes through to thepigmented layer, so that adequate absorption can take place there.

Examples of olefinic polymers of the second outer layer are

propylene homopolymers

a copolymer of

ethylene and propylene or

ethylene and 1-butylene or

propylene and 1-butylene or

a terpolymer of

ethylene and propylene and 1-butylene or

a mixture or blend of two or more of the said homopolymers, copolymersand terpolymers,

particular preference being given for the second outer layer too to thepolymers preferred above for the pigmented outer layer. In addition,polyethylenes, such as HDPE, MDPE or LDPE, if desired mixed with thepropylene polymers for the second outer layer, are also suitable.

The above-described copolymers and/or terpolymers employed in the secondouter layer generally have a melt flow index of from 1.5 to 30 g/10 min,preferably from 3 to 15 g/10 min. The melting point is in the range from120 to 140° C. The above-described blend of copolymers and terpolymershas a melt flow index of from 5 to 9 g/10 min and a melting point offrom 120 to 150° C. All the above-mentioned melt flow indices aremeasured at 230° C. and a force of 21.6 N (DIN 53 735).

If desired, additives, such as antistatics, neutralizers, lubricantsand/or stabilizers, and, if desired, additionally antiblocking agents ineffective amounts in each case can be added to the second outer layer ina manner known per se.

In a further embodiment, the second outer layer may also comprise apigment which absorbs in the wavelength range of laser radiation. In anembodiment of this type, however, it is essential that these laserpigments of the second outer layer absorb in a different wavelengthrange than the laser pigment of the opposite outer layer. A film of thistype can be employed particularly advantageously in combined processesin which on the one hand a seal seam is produced by means of a laser andin addition other processing steps, such as laser cutting, laser markingand/or laser perforation, are used by means of a second laser. Inprocesses of this type, use is made of lasers which have differentwavelengths.

The base layer of the multilayered film comprises essentially apolyolefin, preferably a propylene polymer, and, if desired, opacifyingfillers as well as, if desired, further additives in effective amountsin each case. In general, the base layer comprises at least 50% byweight, preferably from 60 to 99% by weight, in particular from 70 to98% by weight, of the polyolefin, in each case based on the weight ofthe layer.

Preferred polyolefins are propylene polymers. These propylene polymerscomprise from 90 to 100% by weight, preferably from 95 to 100% byweight, in particular from 98 to 100% by weight, of propylene units andhave a melting point of 120° C. or above, preferably from 150 to 170°C., and generally have a melt flow index of from 0.5 to 8 g/10 min,preferably from 2 to 5 g/10 min, at 230° C. and a force of 21.6 N (DIN53 735). Isotactic propylene homopolymer having an atactic content of15% by weight or less, copolymers of ethylene and propylene having anethylene content of 10% by weight or less, copolymers of propylene withC₄-C₈-α-olefins having an α-olefin content of 10% by weight or less,terpolymers of propylene, ethylene and butylene having an ethylenecontent of 10% by weight or less and having a butylene content of 15% byweight or less are preferred propylene polymers for the core layer,particular preference being given to isotactic propylene homopolymer.The stated percentages by weight are based on the respective polymer.

Also suitable is a mixture of the said propylene homopolymers and/orcopolymers and/or terpolymers and other polyolefins, in particular madefrom monomers having from 2 to 6 carbon atoms, where the mixturecomprises at least 50% by weight, in particular at least 75% by weight,of propylene polymer. Suitable other polyolefins in the polymer mixtureare polyethylenes, in particular HDPE, LDPE, VLDPE and LLDPE, where theproportion of these polyolefins in each case does not exceed 15% byweight, based on the polymer mixture.

For opaque embodiments, the opaque base layer of the film comprisesfillers in an amount of at most 40% by weight, preferably from 1 to 30%by weight, in particular from 2 to 20% by weight, based on the weight ofthe opaque layer. For the purposes of the present invention, fillers arepigments and/or vacuole-initiating particles.

For the purposes of the present invention, pigments of the base layerare incompatible particles which result in essentially no vacuoleformation on stretching of the film and generally have a mean particlediameter in the range from 0.01 to a maximum of 1 μm. The base layergenerally comprises pigments in an amount of from 0.5 to 10% by weight,preferably from 1 to 8% by weight. Conventional pigments are, forexample, aluminium oxide, aluminium sulphate, barium sulphate, calciumcarbonate, magnesium carbonate, silicates, such as aluminium silicate(kaolin clay) and magnesium silicate (talc), silicon dioxide andtitanium dioxide, of which white pigments, such as titanium dioxide,calcium carbonate, silicon dioxide and barium sulphate, are preferablyemployed.

“Vacuole-initiating fillers” are solid particles which are incompatiblewith the polymer matrix and result in the formation of vacuole-likecavities on stretching of the films. In general, the vacuole-initiatingfillers have a minimum size of 1 μm. In general, the mean particlediameter of the particles is from 1 to 6 μm. Vacuole-initiating fillersare present in an amount of from 0.5 to 25% by weight, preferably from 1to 15% by weight. Conventional vacuole-initiating fillers are inorganicand/or organic, polypropylene-incompatible materials, such as aluminiumoxide, aluminium sulphate, barium sulphate, calcium carbonate, magnesiumcarbonate, silicates, such as aluminium silicate (kaolin clay) andmagnesium silicate (talc), and silicon dioxide, of which calciumcarbonate and silicon dioxide are preferably employed.

Suitable organic fillers are the polymers usually used which areincompatible with the polymer of the base layer, in particular thosesuch as HDPE, copolymers of cyclic olefins, such as norbornene ortetracyclo-dodecene with ethylene or propene (COC), polyesters,polystyrenes, poly-amides and halogenated organic polymers, preferencebeing given to polyesters, such as, for example, polybutyleneterephthalates and cyclo-olefin copolymers. For the purposes of thepresent invention, “incompatible materials or incompatible polymers”means that the material or polymer is present in the film in the form ofseparate particles or a separate phase.

The film according to the invention comprises at least one outer layerwhich comprises laser pigment. Overall, the film preferably has athree-, four- or five-layered structure. It is preferred for all otherlayers to be substantially transparent to the laser radiation used.

The thickness of the first laser pigment-containing outer layer(s) isgenerally greater than 0.1 μm and is preferably in the range from 0.3 to6 μm. The second, opposite outer layer may be of the same or differentthickness. Its thickness is preferably in the range from 0.3 to 3 μm.

The interlayer(s) may consist of the olefinic polymers described for thebase layer. The interlayer(s) may comprise the conventional additivesdescribed for the individual layers, such as antistatics, neutralizers,lubricants and/or stabilizers, and, if desired, antiblocking agents. Thethickness of the interlayer(s) is greater than 0.3 μm and is preferablyin the range from 1.0 to 15 μm, in particular from 1.5 to 10 μm.

The total thickness of the polyolefin film according to the inventioncan vary within broad limits and depends on the intended use. It ispreferably from 4 to 100 μm, in particular from 5 to 80 μm, preferablyfrom 10 to 50 μm, with the base layer generally making up from about 40to 100% of the total film thickness.

The invention furthermore relates to a process for the production of thepolyolefin film according to the invention by the coextrusion processknown per se, by the flat-film process or by the film blowing process.

The flat film process is carried out by coextruding the meltscorresponding to the individual layers of the film through a flat-filmdie, taking off the resultant film over one or more roll(s) forsolidification, subsequently stretching (orienting) the film,heat-setting the stretched film and, if desired, corona- orheat-treating the surface layer intended for the treatment.

The biaxial stretching (orientation) is carried out sequentially orsimultaneously. Consecutive biaxial stretching, in which stretching isfirstly carried out longitudinally (in the machine direction) and thentransversely (perpendicular to the machine direction), is preferred. Thesimultaneous stretching can be carried out by the flat-film process, forexample by means of LISIM® technology, or by the blowing process. Thefilm production is described further using the example of flat-filmextrusion with subsequent sequential stretching.

Firstly, the polymer or the polymer mixture of the individual layers iscompressed and liquefied in an extruder, it being possible for the laserpigments and any other additives optionally added already to be presentin the polymer or polymer mixture. The melts are then forcedsimultaneously through a flat-film die (slot die), and the extrudedmultilayered film is taken off over one or more take-off rolls at atemperature of from 10 to 100° C., preferably from 20 to 50° C., duringwhich it cools and solidifies.

The film obtained in this way is then stretched longitudinally andtransversely to the extrusion direction, which results in alignment ofthe molecule chains. The longitudinal stretching is advantageouslycarried out with the aid of two rolls running at different speedscorresponding to the target stretching ratio, and the transversestretching is advantageously carried out with the aid of an appropriatetenter frame. The longitudinal stretching ratios are in the range from 4to 8, preferably from 5 to 6. The transverse stretching ratios are inthe range from 5 to 10, preferably from 7 to 9. The longitudinalstretching is preferably carried out at from 80 to 150° C. and thetransverse stretching is preferably carried out at from 120 to 170° C.

The stretching of the film is followed by heat-setting (heat treatment)thereof, in which the film is held at a temperature of from 100 to 160°C. for from about 0.1 to 10 seconds. The film is subsequently wound upin a conventional manner by means of a wind-up device.

After the biaxial stretching, one or both surface(s) of the film is(are) optionally corona- or flame-treated by one of the known methods.The treatment intensity is generally in the range from 37 to 50 mN/m,preferably from 39 to 45 mN/m. The surface treatment of the film isdescribed here using the following example of corona treatment.

In the corona treatment, an advantageous procedure is to pass the filmbetween two conductor elements serving as electrodes, with such a highvoltage, usually an alternating voltage (from about 5 to 20 kV and from5 to 30 kHz), being applied between the electrodes that spray or coronadischarges are able to occur. Due to the spray or corona discharge, theair above the film surface ionizes and reacts with the molecules of thefilm surface, causing the formation of polar inclusions in theessentially non-polar polymer matrix.

For the production of the packaging according to the invention, thefilms described above are processed, for example, in such a way that thetwo first pigmented outer layers of the film or the first pigmentedouter layer and the second outer layer come into contact with oneanother. During subsequent laser irradiation, the laser beam passesthrough the other layers of the film until it hits the outer layers incontact, one or both of which are pigmented. In this or these outerlayer(s), the incorporated pigments cause the radiation to be absorbed,resulting in warming, in a similar manner to the use of heat-sealingjaws. If the film webs are moved correspondingly or the laser beam ismoved correspondingly, a seam is produced in this way, similar to aheat-seal seam, which is suitable for sealing the package.

Suitable for the generation of the laser beam are commercially availableNd:YAG, diode, eximer or CO₂ lasers, whose power is matched to the typeof polymer, the processing speeds and the type of pigment in the outerlayer. In principle, both pulsed and continuously operated lasers can beemployed. Diode lasers in particular are particularly favourable owingto their robustness and wavelength in the near infrared. The width ofthe areas to be sealed can be set by varying the laser focus. Acorresponding adjustment of the energy density of the laser isnecessary. The laser beam generated is focused on the film to be sealedby aperture diaphragms and by means of suitable optics. Correspondingdiaphragms make it possible to generate parallel laser beams in order toapply a plurality of weld and seal seams in a single operation. Ifdesired, it is also possible here to integrate further processing steps,such as, for example, cutting and perforation, into this operation.

Surprisingly, it has been found that the interaction between laser andfilm can be controlled in such a way that on the one hand the laser beamis not already absorbed in the base layer, but instead passes throughthe other layers unhindered in the desired manner, but on the other handthe absorption cross section in the corresponding outer layer issufficiently large to effect melting of the outer layer and thus toproduce a seal seam. The absorption cross section here is, surprisingly,sufficiently large that the packaged product, in particular alsoheat-sensitive product, is not damaged by the laser beam.

The raw materials and films were characterized using the followingmeasurement methods:

Melt Flow Index

The melt flow index was measured in accordance with DIN 53 735 at a loadof 21.6 N and 230° C.

Mean Particle Size

The mean particle size was determined by image analysis. For thispurpose, a sample is dispersed in water in order to separate theparticles and applied to a glass slide. The sample is subsequently driedand studied under the scanning electron microscope. For this purpose,the individual particles are visualized as a gray shade image by meansof a suitable setting of brightness and contrast. Over an area of 10mm², the respective area of the separated particles is measured, and theparticle diameter output as the diameter of a circle of equal area.These measurement values are classified by size ranges and indicate thedistribution of the particle size. The mean particle diameter isdetermined as the mean of the distribution curve.

Melting Point

DSC measurement, maximum of the melting curve, heating rate 20° C./min.

The invention is explained below by means of working examples.

COMPARATIVE EXAMPLE 1

An opaque five-layered film having an asymmetrical structure and a totalthickness of 33 μm was produced by coextrusion and subsequent stepwiseorientation in the longitudinal and transverse directions. The outerlayer A had a thickness of 1.2 μm and the underlying interlayer B had athickness of 3.5 μm. The outer layer E had a thickness of 0.5 μm and theunderlying interlayer D had a thickness of 0.1 μm. The layers had, indetail, the following composition:

Base layer: 87.0% by weight of isotactic propylene homopolymer having amelting point of 159° C. and a melt flow index of 3.4 g/10 min 9.0% byweight of chalk masterbatch (Omyalite 90T) comprising 28% by weight ofpropylene homopolymer and 72% by weight of CaCO₃ Interlayers B and D100% by weight of isotactic propylene homopolymer having a melting pointof 150° C. and a melt flow index of 3.4 g/10 min Outer layer A 100% byweight of random C₂-C₃-copolymer comprising 5% by weight of ethylene andhaving a crystallite melting point of 125° C. and a melt flow index of6.5 g/10 Outer layer E: 98.8% by weight of randomethylene-propylene-butylene terpolymer having an ethylene content of 3%by weight and a butylene content of 7% by weight (remainder propylene)and having a crystallite melting point of [lacuna] and a melt flow indexof [lacuna]

The production conditions in the individual process steps were asfollows:

Extrusion: Temperatures Base layer: 260° C. Interlayers: 255° C. Outerlayers: 240° C. Temperature of the take-off roll:  20° C. Longitudinalstretching: Temperature: 110° C. Longitudinal stretching ratio:  5.5Transverse stretching: Temperature: 160° C. Transverse stretching ratio: 9 Setting: Temperature: 150° C. Convergence:  5%

EXAMPLE 1

A film was produced as described in Comparative Example 1. In contrastto Comparative Example 1, the film comprised 0.6% by weight, based onthe weight of the layer, of carbon black in outer layer E. The remainderof the composition and the production conditions were unchanged comparedwith Comparative Example 1.

EXAMPLE 2

A film was produced as described in Comparative Example 1. In contrastto Comparative Example 1, outer layer E now comprised a mixture ofcarbon black and rutile (TiO₂) in the ratio (weight ratio) 1:1. Thetotal content of carbon black and rutile in outer layer E was 0.6% byweight, based on the weight of outer layer E. The remainder of thecomposition and the production conditions were unchanged compared withComparative Example 1.

EXAMPLE 3

A film was produced as described in Comparative Example 1. In contrastto Comparative Example 1, outer layer E now comprised 0.8% by weight ofsilver pigment, based on the weight of the layer, which consists ofaluminium platelets. The remainder of the composition and the productionconditions were unchanged compared with Comparative Example 1.

COMPARATIVE EXAMPLE 2

A film was produced as described in Comparative Example 1. In contrastto Comparative Example 1, the film comprised 2.5% by weight, based onthe weight of the layer, of fine chalk (Socal) in outer layer E. Theremainder of the composition and the production conditions wereunchanged compared with Comparative Example 1.

COMPARATIVE EXAMPLE 3

A film was produced as described in Comparative Example 1. In contrastto Comparative Example 1, the film comprised 2.5% by weight, based onthe weight of the layer, of a feldspar (Minex) in outer layer E. Theremainder of the composition and the production conditions wereunchanged compared with Comparative Example 1.

EXAMPLE 4

A film was produced as described in Comparative Example 1. In contrastto Comparative Example 1, the film comprised 1.0% by weight, based onthe weight of the layer, of a copper alloy with zinc as gold pigment inouter layer E. The remainder of the composition and the productionconditions were unchanged compared with Comparative Example 1.

EXAMPLE 5 Copolymer Outer Layer Variant

A film was produced as described in Comparative Example 1. In contrastto Comparative Example 1, the film comprised 0.8% by weight of silverpigment, based on the layer, in outer layer A. The remainder of thecomposition and the production conditions were unchanged compared withComparative Example 1.

The films produced as described in the examples and comparative exampleswere laid one on top of the other in two layers on a metal plate. Thefilm layers were arranged in such a way that the film located directlyon the metal plate lay on the metal plate with the unpigmented outerlayer (outer layer A for CE 1 to 3 and Example 1 to 4; outer layer E forExample 5) and the opposite pigmented outer layer was in contact withthe second film layer. The second film layer made from the same film wasarranged in such a way that its pigmented outer layer was in contactwith the pigmented outer layer of the first film layer. The twopigment-containing outer layers were thus in contact. In addition, atransparent polyethylene plate was laid on the two film layers andpressed the two film layers gently against one another. This arrangementwas then irradiated both continuously by means of a diode laser at awavelength of 980 nm and with a laser power of from 15 to 25 W and alsoby means of a CO₂ laser (10600 nm) with a power of from about 50 to 80 Wwith a pulse duration of from 10 to 14 μs. During the irradiation, thefilm layers were pulled through the two plates at a constant speed witha gentle contact pressure. The speed was varied in a range of 0.4-4m/min.

On use of a CO₂ laser, a line-shaped seal seam with good strength wasformed in the case of all films. At the same time, deformation of theseal seam caused by melting of the entire film and damage to the filmsurface are evident.

The irradiation with a diode laser likewise caused a line-shaped “sealseam” in the case of the carbon black- and aluminium-pigmented films inaccordance with the examples, while in the case of the samples inaccordance with the comparative examples, the laser beam passed throughthe films without producing any evident effect. A somewhat higher laserpower was necessary to produce a sufficiently strong seal seam in thecase of the films according to Example 5. Comparison of Example 3 withExample 5 shows that a higher laser energy is necessary to achieve aspecified seal seam strength due to the use of a higher-melting sealingraw material (copolymer).

In detail, it was observed that the films in accordance with theexamples exhibited good adhesive strength in the welded area. Throughslight changes in the feed rate of the films, it was possible to achievea variation in the seal seam width.

What is claimed is:
 1. A packaging made of a multilayered, orientedpolyolefin film which film comprises a base layer and at least one firstouter layer, wherein the polyolefin film comprises in the first outerlayer an additive which has an absorption in the wavelength range oflasers such that, on local irradiation of the film with a laser, atemperature increase occurs in the area of the irradiation such that thepolyolefin of the first outer layer softens or melts therein in theirradiated area and bonds to a further layer on cooling, wherein thefilm is transparent.
 2. A packaging made of a multilayered, orientedpolyolefin film which film comprises a base lever and at least one firstouter layer, wherein the polyolefin film comprises in the first outerlayer an additive which has an absorption in the wavelength range oflasers such that, on local irradiation of the film with a laser, atemperature increase occurs in the area of the irradiation such that thepolyolefin of the first outer layer softens or melts therein in theirradiated area and bonds to a further layer on cooling, wherein thefilm has an opaque base layer which comprises vacuole-initiatingfillers.
 3. Packaging according to claims 1 or 2, wherein the outerlayer comprises at least about 80% by weight of a propylene polymer. 4.Packaging according to claim 3, wherein the propylene polymer is anethylene-propylene copolymer or a terpolymer.
 5. Packaging according toclaims 1 or 2 wherein the additive is present in an amount of from about0.01 to about 10% by weight, based on the weight of the first outerlayer, and the mean particle diameter is from about 0.01 to about 4 μm.6. Packaging according to claims 1 or 2 wherein the thickness of thefirst outer layer is from about 0.1 to about 5 μm.
 7. Packagingaccording to claims 1 or 2, wherein the additive is a laser-absorbentmetal, black or coloured pigment.
 8. Packaging according to claims 1 or2 wherein the film has, on the opposite side, a second outer layer whichcomprises an additive which absorbs radiation in the wavelength range ofa laser, where the additives of this second outer layer absorb in adifferent wavelength range than the additives of the first outer layer.9. Packaging according to claims 1 or 2, wherein the film only comprisesan additive which absorbs radiation in the wavelength range of a laserin the first outer layer and in no other layer.
 10. A multilayered,oriented polyolefin film which comprises a base layer and at least onefirst outer layer, wherein the first outer layer comprises a pigmentcomprising a copper alloy.
 11. Multilayered, oriented polyolefin film,according to claim 10, wherein the copper alloy is a copper/zinc alloy,and the pigment is in an amount of from about 0.5 to about 3% by weight,based on the weight of the outer layer.
 12. Multilayered, orientedpolyolefin film, according to claim 10, wherein the other layers of thefilm do not comprise any pigment which absorbs radiation in thewavelength range of a laser.
 13. Multilayered, oriented polyolefin film,according to claim 10, wherein the first outer layer additionallycomprises a white pigment.
 14. Multilayered, oriented polyolefin film,according to claim 13, wherein the white pigment is TiO₂. 15.Multilayered, oriented polyolefin film, according to claim 10, whereinthe base layer comprises fillers in an amount of up to about 40% byweight.
 16. Multilayered, oriented polyolefin film, according to claim15, wherein the filler is CaCO₃, TiO₂, polyethylene terephthalate orpolybutylene terephthalate.
 17. A process for the production of apackaging made of a multilayered, oriented polyolefin film whichcomprises a base layer and at least one first outer layer, wherein thepolyolefin film comprisies in the first outer layer an additive whichabsorbs in the wavelength range of lasers, which process comprises thesteps of irradiating the polyolefin film with a laser such that a localtemperature increase occurs in the area of the irradiation, and thepolyolefin of the first outer layer softens or melts therein in theirradiated area and bonding said polyolefin to a further layer oncooling.
 18. Process according to claim 17, wherein the polyolefin filmhas a second, opposite outer layer and has in this second outer layer anadditive which absorbs in the wavelength range of a laser, furthercomprising the step of producing a seam for sealing the packaging bymeans of a laser having a first wavelength range and then marking and/orcutting and/or perforating the film by means of a second laser havinganother wavelength range which is different from that of the firstlaser.
 19. Process according to claim 18, wherein the working by meansof a plurality of lasers of different wavelength is carried outsimultaneously.
 20. A process for the production of packaging comprisinga container with a lid, where the lid lies on a container rim and wherethis lid is made of a multilayered, oriented polyolefin film, where thefilm comprises a base layer and at least on first outer layer and wherethis first outer layer is in contact with the container rim, wherein thefilm in the first outer layer comprises an additive which has anabsorption in the wavelength range of a laser which process comprisesthe steps of such that, irradiating the film with this laser, such thata temparature increase occurs In the first outer layer and thepolyolefin of the first outer layer softens or melts in this area andbonding said film to the container rim on cooling.